The invention relates to a method for the integral leak detection on test samples comprising a test gas with relatively thin walls, in which the test samples are examined for leaks in a test chamber.
From DE-A-196 42 099 a film leak detector is known. The test for impermeability takes place in such manner that the test sample comprising test gas being examined for leaks is introduced into a test chamber formed by two expandible films. This prior known device is in particular suitable for testing the impermeability of the packaging of packaged food items (chocolate bars, coffee, etc.), pharmaceutical agents (for example tablets) or objects aseptically packaged for use in medical practice, etc. The packaging of these items must be impermeable since atmospheric oxygen or microbes must be kept from penetrating the product. In particular packaged products of this type are referred to in the present application as test samples with relatively thin walls. The packaging forms the xe2x80x9cthin wallxe2x80x9d. As a rule, helium serves as the test gas.
In the case of test samples of this type, which are produced in large production numbers, leak detection can only be carried out in the manner of random sampling. If from a test sample subjected to a random sampling no test gas is emitted, the following possibilities exist:
it is impermeable;
it is grossly permeable (the test gas has already leaked out before the test sample had reached the test chamber;
it is permeable; however, it contains no test gas.
In order to be able to interpret the measuring result better, at the conclusion of the impermeability test a test gas concentration measurement of the gas atmosphere of the content of the packaging would have to be carried out. In the simplest case this could take place by inserting a suitable probe of a sniffing leak detector. However, the smaller the gas volume in the test sample, the more uncertain this checking step becomes. A small volume of gas contained in the packaging is drawn off relatively rapidly by the sniffing probe and can either not be demonstrated at all or at least not completely. In addition, the danger exists of obstructing the sniffing probe if there are powder-form products in the test sample.
The present invention is based on the task of providing, in the case of a method of the type discussed in the introduction, a checking step which is improved with respect to its certainty and reliability.
This task is solved according to the invention thereby that for checking the test gas concentration in the test samples, the test gas concentration is measured in at least one of the test samples thereby that the wall of this test sample is provided with a leak, and that a leak detection process is carried out with this test sample. The test sample serving for checking the test gas concentration is usefully a test sample which in a preceding leak detection process had been demonstrated to be impermeable.
If examination of the test sample provided with the leak reveals that it contains test gas in the desired concentration, its packaging was impermeable before the generation of the leak. Based thereon the conclusion can be drawn that all other test samples of this series are impermeable. If the test sample serving for checking the test gas concentration does not contain the desired test gas concentration, it is probable that production errors have occurred, be that that the packaging is permeable or that the test sample had not been filled properly with test gas.
Generating a sufficiently small leak in the wall of a test sample is difficult. The insertion of a relatively thin needle already generates a gross leak, which no longer permits reliable concentration measurements. The danger exists that the test gas already leaks completely out of the test sample at the beginning of the leak detection cycle, thus during the evacuation of the test chamber and before switching to the leak measurement. Within the scope of the invention, it is further proposed to provide the test sample with a defined leak. This is accomplished thereby that the test sample to be examined, for example, is pierced with a needle and subsequently the hole is immediately closed with a patch leak. Since, as a rule, the total pressure within and outside of the packaging is identical or at least not significantly different, there are no changes between the piercing and the application of the patch leak or only minor ones in terms of the concentration in the test sample. Subsequently, a new leak detection is carried out in the test chamber. The patch leak represents a defined permeability. This permeability is so slight that during the test the concentration in the packaging does not change. The leak rate signal displayed in this test is a measure of the test gas concentration in the package.